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Free, publiclyaccessible full text available February 22, 2024

WinnerTakeAll (WTA) refers to the neural operation that selects a (typically small) group of neurons from a large neuron pool. It is conjectured to underlie many of the brain’s fundamental computational abilities.However, not much is known about the robustness of a spikebased WTA network to the inherent randomness of the input spike trains. In this work, we consider a spikebased k–WTA model where in n randomly generated input spike trains compete with each other based on their underlying firing rates, and k winners are supposed to be selected. We slot the time evenly with each time slot of length 1ms, and model then input spike trains as n independent Bernoulli processes. We analytically characterize the minimum waiting time needed so that a target minimax decision accuracy (success probability) can be reached.We first derive an informationtheoretic lower bound on the decision time. We show that to guarantee a (minimax) decision error≤δ(whereδ∈(0,1)), the waiting time of any WTA circuit is at least((1−δ) log(k(n−k) + 1)−1)TR,whereR ⊆(0,1) is a finite set of rates, and TR is a difficulty parameter of a WTA task with respect to setRfor independent input spike trains.Additionally,TR is independent ofδ,n, andk. We then design a simple WTA circuit whose waiting time isO((log(1δ)+ logk(n−k))TR), provided that the local memory of each output neuron is sufficiently long. It turns out that for any fixed δ, this decision time is orderoptimal (i.e., it 2 matches the above lower bound up to a multiplicative constant factor) in terms of its scaling inn,k, and TR.more » « less

We consider multiarmed bandit problems in social groups wherein each individual has bounded memory and shares the common goal of learning the best arm/option. We say an individual learns the best option if eventually (as $t\diverge$) it pulls only the arm with the highest expected reward. While this goal is provably impossible for an isolated individual due to bounded memory, we show that, in social groups, this goal can be achieved easily with the aid of social persuasion (i.e., communication) as long as the communication networks/graphs satisfy some mild conditions. In this work, we model and analyze a type of learning dynamics which are wellobserved in social groups. Specifically, under the learning dynamics of interest, an individual sequentially decides on which arm to pull next based on not only its private reward feedback but also the suggestion provided by a randomly chosen neighbor. To deal with the interplay between the randomness in the rewards and in the social interaction, we employ the \em meanfield approximation method. Considering the possibility that the individuals in the networks may not be exchangeable when the communication networks are not cliques, we go beyond the classic meanfield techniques and apply a refined version of meanfield approximation: Using coupling we show that, if the communication graph is connected and is either regular or has doublystochastic degreeweighted adjacency matrix, with probability → 1 as the social group size N → ∞, every individual in the social group learns the best option. If the minimum degree of the graph diverges as N → ∞, over an arbitrary but given finite time horizon, the sample paths describing the opinion evolutions of the individuals are asymptotically independent. In addition, the proportions of the population with different opinions converge to the unique solution of a system of ODEs. Interestingly, the obtained system of ODEs are invariant to the structures of the communication graphs. In the solution of the obtained ODEs, the proportion of the population holding the correct opinion converges to 1 exponentially fast in time. Notably, our results hold even if the communication graphs are highly sparse.more » « less

Winnertakeall (WTA) refers to the neural operation that selects a (typically small) group of neurons from a large neuron pool. It is conjectured to underlie many of the brain’s fundamental computational abilities. However, not much is known about the robustness of a spikebased WTA network to the inherent randomness of the input spike trains.In this work, we consider a spikebased k–WTA model wherein n randomly generated input spike trains compete with each other based on their underlying firing rates and k winners are supposed to be selected. We slot the time evenly with each time slot of length 1 ms and model then input spike trains as n independent Bernoulli processes. We analytically characterize the minimum waiting time needed so that a target minimax decision accuracy (success probability) can be reached. We first derive an informationtheoretic lower bound on the waiting time. We show that to guarantee a (minimax) decision error≤δ(whereδ∈(0,1)), the waiting time of any WTA circuit is at least ((1−δ)log(k(n−k)+1)−1)TR,where R⊆(0,1)is a finite set of rates and TR is a difficulty parameter of a WTA task with respect to set R for independent input spike trains. Additionally,TR is independent of δ,n,and k. We then design a simple WTA circuit whose waiting time is 2524L. Su, C.J. Chang, and N. Lynch O((log(1δ)+logk(n−k))TR),provided that the local memory of each output neuron is sufficiently long. It turns out that for any fixed δ, this decision time is orderoptimal (i.e., it matches the above lower bound up to a multiplicative constant factor) in terms of its scaling inn,k, and TR.more » « less